1. Field of the Invention
The invention relates to a method of fabricating an integrated circuit, and more particularly, to a method of controlling a threshold voltage and a method of fabricating a semiconductor device.
2. Description of Related Art
Threshold voltage (Vt) is used for determining the reference voltage of turning on and off a transistor. In order to match the electrical properties of the various transistors in the integrated circuit with the same voltage source, the control of the threshold voltage is relatively important in the fabrication of ICs, especially to the current designs of low power and low voltage. Currently, the adjustment of the threshold voltage is done through an ion implantation process, wherein the parameter of the ion implantation is adjusted according to an empirical value and the dopant is formed on the surface of the substrate. However, the doping concentration and the uniformity of each wafer cannot be accurately controlled by adjusting the parameter of the ion implantation according to the empirical value. As a result, the uniformity of the threshold voltage between wafers is poor.